In a semiconductor integrated circuit such as a microprocessor unit, a DC voltage supplied from an electronic circuit substrate on which the semiconductor integrated circuit is mounted is stepped down and converted into a voltage corresponding to the wiring width of a semiconductor circuit or the like. Although there are various types of step-down DC-DC converters for converting the voltage in this manner, the synchronous rectification type is often used for microprocessor units and the like due to excellent efficiency.
For example, a synchronous rectification step-down DC-DC converter described in Patent Literature 1 includes a switching circuit device having a high-side switching element and a low-side switching element connected in series between a high-voltage terminal of a high voltage source that outputs a voltage of a conversion source and the ground and a drive circuit or the like for turning on and off these elements, and includes a smoothing circuit connected to a connection point of the high-side switching element and the low-side switching element and configured to smooth the voltage output from the switching circuit device. A p-type MOSFET (metal-oxide-semiconductor field-effect transistor) is used as the high-side switching element connected to the high-voltage terminal side, and an n-type MOSFET is used as the low-side switching element connected to the ground (low-voltage) side.